The present invention relates to the use of porphyrin derivatives for containing algae growth and controlling bacterial germs in aquaria.
Due to the growing demand for clean water at a time when its availability from natural sources is stagnant or decreasing, the development of methods for water processing has become increasingly important in the past decades. Numerous processes are already known aimed for example at eliminating bacterial contamination of water. Strong oxidizing agents such as hypohalogenites or permanganate are frequently used in the supply of potable water. Apart from these processes, methods such as the treatment of water with ozone or UV-radiation, which are aimed at preventing the water quality from being affected by added chemicals, are becoming increasingly significant.
However, such processes, which most of the time can only be carried out at a large scale and considerable technical expense, can generally not do justice to the requirements in the field of aquaria, where special demands to the applied water processing methods have to be met. While in conventional methods which are applied to free the treated water as completely as possible from microorganisms present therein there is the possibility of reprocessing the water prior to supplying it to the consumer, application in an aquarium requires a substance that can be used continuously and in situ without affecting the fauna and flora. In general, filtration systems are used to purify the aquarium water, wherein the filters mainly remove particulate impurities from the water (mechanical filtration). Additionally, chemical filters in the form of ion exchangers are often employed for controlling the ionic composition of the water. However, even the use of further chemically effective filtering substances such as for example activated carbon cannot always effectively prevent the occurrence and propagation of bacterial contaminants.
Controlling the water quality in an aquarium allows to prevent algae growth on the one hand and the occurrence of diseases in fish on the other hand. In particular in the case of bacterial diseases in fish, it is desirable to have an effective means at hand to counteract the spread of pathogens early on since sensitive fish species do not always respond successfully to medical treatments. The presence of numerous bacterial pathogens in water has been verified, including gram-positive rod-shaped and coccal bacteria, aeromonads, mycobacteria, gram-negative rod-shaped bacteria, vibrios and pseudomonads. The purposeful use of antibiotics against such bacteria cannot be initiated until first symptoms of the disease appear and additionally requires an exact identification of the pathogen. At that point, a propagation of the disease can no longer be prevented effectively.
Document DE-A-196 06 081 describes an application in a related field, namely the treatment of water in fish breeding plants wherein photosensitizers are used for disinfecting the water. However, contact of the fish with the sensitizers is prevented at great expense; the water is moved to a separate container for sterilization, irradiated and subsequently led back into the fish basins.
The object underlying the present invention is therefore the provision of an agent for controlling algae and bacterial germs in aquaria without the need for additional devices.
According to the present invention, this object is achieved by introducing at least one photosensitizer of the tetrapyrrol and/or tetraazopyrrol families having at least one positive charge into the water and subjecting it to electromagnetic radiation, preferably light. Although they are for example also known as stomach poisons for insects, the mentioned compounds can be added directly to the water in the aquarium without affecting the fish or the plants therein.
Due to their ability of catalyzing the formation of excited molecules upon irradiation, the use of such photosensitizers in the aquarium water can advantageously prevent the spread of monocellular or multicellular algae or bacteria in the aquarium.
Both gram-positive and gram-negative bacteria can successfully be controlled by the use of the sensitizers according to the present invention. In particular, however, compared to alternative processes, the method of the present invention offers the advantage that gram-negative bacteria, which are resistant to numerous other chemicals, can very effectively be controlled with the photosensitizers.
The term xe2x80x9cphotosensitizersxe2x80x9d in the present invention denotes compounds which absorb electromagnetic radiation, preferably visible light, and are able to catalyze the formation of radicals and/or singlet oxygen from triplet oxygen under the influence of radiation. Tetrapyrrol and/or tetraazopyrrol compounds having at least one positively charged substituent (cationic photosensitizers) are suitable for use in the present invention. The type of substituent at the macrocyle is of secondary importance for the photochemical properties of the photosensitizers; they essentially influence their solubility properties. Thus, by purposefully introducing certain substituents, the desired solubility properties can be imparted to the photosensitizers while retaining the photochemical properties of the starting compound. A number of commercially available compounds suitable for this purpose are already at the disposal of the person skilled in the art.
When a photosensitizer of the above type is irradiated, preferably with light, it unfolds its antibacterial effect via the activation of oxygen and/or the promotion of processes involving radicals. Preferably, the radiation has a spectrum in the range of about 350 to 900 nm.
The inventive use of the photosensitizers exhibits a good effectiveness for controlling a number of gram-negative bacteria. Typical examples of gram-negative bacteria which are deactivated quickly and efficiently by irradiation with visible light in the presence of cationic photosensitizers include Escherichia coli, Pseudomonas aeroginosa and Vibrio anguillarum. On the other hand, such sensitizers can also deactivate gram-positive bacteria such as staphylococci and streptococci. The positive charge necessary for antibacterial activity can be introduced into the macrocycle by way of different substituents.
Preferred substituents for introducing the positive charge into the molecule carry a quaternary ammonium group or a heterocycle comprising a positively charged nitrogen atom.
Especially preferred substituents comprise at least one trialkylammonium group. Furthermore, N-alkyl-pyridinium, N,N-dialkyl-piperazinium or N,N-dialkyl-piperidinium derivatives are preferably used as positively charged substituents. The number of positively charged substituents is preferably in the range of 1 to 4. The positive charge of the macrocycle can be neutralized by anions such as halide ions or tosylate.